Well this isn't about dirtbike engines it's about lawnmower engines. Not to long ago our riding lawnmower started to idle a little funny. Now it doesn't idle it revs up then slows down revs up then slows down . What causes this. I know when the engine slows down the governor kicks in to rev the engine why it won't idle correctly. Now it seems to do this to a lesser extent at full throttle. I find a little choke doesn't hurt to be on. I guess a good cleaning would be in order? Next question. What would cause a chainsaw to stop running when it warms up. As soon as it warms up 1-2min it would just quit. You couldn't start it until it was cold again. Buddy took it the small engine shop and they said they had to replace a part and now it works great.